1. Field of the Invention
The present invention relates to a printing apparatus.
2. Description of the Related Art
An inkjet type printing apparatus (to be simply referred to as an inkjet printing apparatus hereinafter) which discharges ink to form and print dots on a printing medium is known. Such a printing apparatus includes a conveyance mechanism which conveys a printing medium. The conveyance mechanism includes, for example, a conveyance roller and a pinch roller driven by it. Known examples of the conveyance method of the conveyance mechanism are a scheme in which a printing medium is conveyed while being pinched between the conveyance roller and the pinch roller, and a belt conveyance scheme in which a printing medium is conveyed together with a belt while being attracted to the belt. A known method of attracting a printing medium to a belt in the belt conveyance scheme is an electrostatic scheme in which a voltage is applied to a belt to attract a printing medium using the electrostatic force generated by the belt.
An inkjet printing apparatus often adopts the so-called mariginless print function of printing an image on the entire surface of a printing medium. In mariginless printing, ink is discharged to fall outside the edge of a printing medium by taking account of landing errors of the ink encountered when it lands on the printing medium. In view of this, it is often the case that when a printing apparatus which adopts the belt conveyance scheme performs mariginless printing, ink discharged to fall outside the edge of a printing medium contaminates the belt surface.
To combat this situation, cleaning mechanisms which remove the ink that causes such contamination are known. One cleaning mechanism scrapes the ink adhering on the conveyance belt by a blade. In the cleaning mechanism which uses a blade, the ink adhering on the blade undesirably solidifies when, for example, the printing apparatus has not been in use for a long period of time. This often results in a cleaning failure or a conveyance failure such as slipping of the conveyance belt attributed to an increase in its conveyance load. To prevent this, the technique described in Japanese Patent Laid-Open No. 2004-136533 brings the blade into contact with the conveyance belt from its lower side, and recovers the ink, scraped from the conveyance belt, by an absorbing member located on the lower side of the blade.
Also, in the belt conveyance scheme, the conveyance belt may shift and meander due to the adverse effect of factors associated with, for example, the parallelism between the driving roller and driven roller across which the conveyance belt is suspended, and a load imposed on the conveyance belt.
When such a shift of the conveyance belt occurs during a printing process, the actual landing points of the ink may deviate from its ideal landing points in an inkjet printing apparatus and this may degrade the print quality of the apparatus.
To tackle this situation, one known method forcibly suppresses meandering of the belt by disposing a flange serving as a regulating guide member and abutting the belt edge against the flange, as in the technique described in Japanese Patent Laid-Open No. 2004-244198. Another known method detects the amount of meandering of the belt and tilts the belt in accordance with the amount of meandering, as in the technique described in Japanese Patent Laid-Open No. 11-20973. Still another known method suppresses meandering of the belt by locating ribs in the inner periphery of the belt edge.
In this manner, most of various known methods of suppressing meandering of the belt exploit ribs. This is because an arrangement which exploits ribs is relatively simple and this leads to cost reduction and high reliability. However, when meandering is suppressed using ribs, a large stress acts on the ribs. As a result, the ribs may flake off or deform due to wear, or the roller may mount on the ribs due to downward bending of the belt edge. To prevent this, the technique described in Japanese Patent Laid-Open No. 2000-337464 reinforces the portion which receives a stress by adding a reinforcing material to the surface of the conveyance belt at the positions where ribs are present in the inner periphery of the edge of the conveyance belt.
As described above, when a printing medium is conveyed by the belt conveyance scheme, a conveyance failure may occur due to the presence of the ink adhering on the conveyance belt or meandering of the conveyance belt may occur due to a shift of the conveyance belt.
The mechanism disclosed in Japanese Patent Laid-Open No. 2004-136533 as a technique of removing the ink adhering on the conveyance belt still suffers from a problem associated with the situation in which the ink may not fall onto the absorbing member and so may remain on the blade when the amount of scraped ink is relatively small.
Also, the ribs disclosed in Japanese Patent Laid-Open No. 2000-337464 as a technique of suppressing meandering of the conveyance belt are located in the inner periphery of the conveyance belt on both its left and right sides, and this entails a cost higher than that required when a general conveyance belt is used. For cost reduction, another known method locates ribs in the inner periphery of the edge of the conveyance belt on its only one side. The technique described in Japanese Patent Laid-Open No. 2002-23509 locates members on the side on which ribs are located and its opposite side on the conveyance belt to maintain a given balance of the tension of the conveyance belt. Also, the technique described in Japanese Patent Laid-Open No. 2-27383 forms a groove at the same position as that where a rib is present. Still another known method, for example, prevents the conveyance belt from shifting toward the side on which the ribs are located on the conveyance belt. Nevertheless, this method requires separately providing a configuration for maintaining a given balance of the tension of the conveyance belt, and this entails a high cost. In this manner, when a printing medium is conveyed by the belt conveyance scheme, a technique of improving the recovery efficiency of the ink remaining on the blade, and suppressing meandering of the conveyance belt at low cost is desired.